The power demand in a grid varies over time. For different times of a day, varying power output into the grid is needed in order to meet the power consumption demands.
For synchronous generation power plants (like thermal or nuclear ones), the power injected into the grid at a specific time is easily controlled.
However, for wind power plants, the unpredictable nature of the wind renders it more difficult to control the power output from these plants at a given time.
It is known to use diesel generators in the grid for short injections of power into the grid at times needed to stabilize e.g. grid frequency. However, the usage of diesel generators is a supplementary cost and it can not be seen as an environmental friendly alternative.
WO 03/030329 discloses a method for operating a wind park. The wind park is connected to an electric supply network into which the power produced by the wind park is fed. At least one of the wind power plants of the wind park is provided with a control input which is used to adjust the electric power of the wind park or one or several of the individual wind plants in the park within a range of 0-100% of the respectively provided power.
However, a problem with this solution is that the nominal power of a wind power plant is used, which may not be reached in reality.